Wyniki wyszukiwania - Biblioteka Nauki

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„Ekstrakcja” wykorzystująca zjawisko zmętnienia roztworów związków powierzchniowo czynnych

100%

Szymanowski J.

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tom [Z] 52, 7-8

597--613

EN

Nonionic surfactants containing a polyoxyethylene chain 1 and 2 dissolve well in aqueous solutions due to the hydration of the hydrophilic chains. All parameters, e.g. temperature and electrolyte content, which affect the hydration change the solubility of nonionic surfactants in water. As a result, clouding of surfactant solutions is observed after heating them. The process is reversible and nonionic surfactants dissolve after cooling. Aqueous solutions of zwitterionic surfactants (3 and 4) also exhibit the cloud point phenomenon but in this case after cooling. The cloud point temperature depends on several parameters, including the hydrophobicity and polydispersity of surfactants. The presence of additional organic compounds, e.g. alcohols, fatty acids, etc., and type and content of electrolytes. Therefore, the cloud point can be easily modified to cause the clouding separated, e.g. by centrifugation. However, only the knowledge of the surfactant-water phase diagrams (Figs 1 and 2) permits the design of optimal conditions at which the surfactant-rich-phase is in equilibrium with almost pure water. Aqueous solutions of some b-cyclodextrine derivatives (Fig. 3) also exhibit the clouding phenomenon caused, however, by crystallisation. Nonionic surfactants dissolved in organic solvents complex small amounts of ion pairs. As a result, they are considered as open analogs of crown ethers. Aqueous solutions containing surfactants at concentrations above the critical micelle concentration solubilize various organic and inorganic substances, including chelating agents and chelates. Ions can be also sorbed by charged micelles. The spherical micelles of nonionic surfactants (Fig. 4) can be thus considered as dynamic analogs of crown ethers. Typical hydrophobic extractants/chelating agents used in hydrometallurgical processes are exceedingly large and scarcely soluble in aqueous solutions, including micellar solutions, to obtain high enough extractant concentrations. Because of that, hydrophilic complexing agents such as oxine., PAP, PAMP, etc. Are used. Special reagents exhibiting both amphiphilic and chelating properties (5 and 6) can be also used. In this case they act simultaneously as surfactants and chelating agents. The distributions coefficients of chelating agents (Tabs 1 and 2) and their metal complexes (Tab. 3) between the surfactant-rich phase and the aqueous phase are comparable to those observed in classical extraction systems. These are, however, lower in comparison to those obtained for hydrophobic industrial extractants. The recovery of metal ions from diluted aqueous solutions can be near 100% (Tab. 4). The system is also useful to recover various organic substances from aqueous solutions (Tab. 5) and from contaminated soil (Tab. 6). The technique has found already application for sample preconcentration, recovery of toxic substances from solutions and soils and separation of expensive biological materials.

2

Magnetisation and Electron Spin Resonance of the colossal magnetoresistive La0.67Ca0.33Mn1-x FexO3

84%

Zając T. , Folcik L. , Chmist J. , Kołodziejczyk A. , Drulis H. , Krop K. , Gritzner G.

Materials Science Poland

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2006

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tom Vol. 24, No. 3

795--801

EN

We report magnetisation and electron spin resonance (ESR) measurements on colossal magnetoresistive manganites La0.67Ca0.33Mn1-x FexO3 with x = 0, 0.01, 0.03, 0.06, 0.10 and 0.15 in the vicinity of the magnetic (TC) and metal- insulator (TMI) transition temperatures. Above TC the resonance lines with g?2 are caused by the ferromagnetic metallic clusters exhibiting the double exchange interaction between Mn3+-Mn4+ ions. The lines were observed with cooling far below both TC and TMI and were fitted by Dysonian line-shape. Temperature dependences of the linewidths exhibited a minimum value at Tmin?1.25 TC followed by an increase of the width with further cooling toward TC. The anomalous behaviour of the line-width below Tmin is due to an appearance of a ferromagnetic metallic phase within the paramagnetic matrix. The role of phase segregation in which the compounds are phase - separated into a mixture of ferromagnetic and paramagnetic regions is discussed.

3

Sorbenty polimerowe - synteza i właściwości

84%

Trochimczuk A. W.

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tom Vol. 52, nr 25

119-122

PL

Sorbenty polimerowe otrzymywane metodą polimeryzacji suspensyjnej, należą do grupy tzw. polimerów specjalnych. Stosowane są, między innymi, do sorpcji związków organicznych z roztworów wodnych oraz jako nośniki katalizatorów. Właściwości tych materiałów zależą od rodzaju monomerów, użytych do ich otrzymywania oraz od warunków polimeryzacji. W pracy omówiono podstawy syntezy oraz sposoby modyfikowania struktury nadcząsteczkowej sorbentów polimerowych, ze szczególnym uwzględnieniem wyników prac prowadzonych w Instytucie Technologii Organicznej i Tworzyw Sztucznych Politechniki Wrocławskiej.

EN

Polymeric sorbents, obtained through suspension polymerization method, belong to the so-called group of specially polymers. They are applied as adsorbents to remove organic impurities from aqueous solutions and as carriers for catalysts. The properties of these materials depend on the type of monomers used in the synthesis and on polymerization parameters. In this presentation the information about the synthesis and methods used in the modification of crosslinked polymers are given with the particular attention to the research work done in the Institute of organic and Polymer Technology, Wroclav University of Technology.

4

Application of the Euler characteristic to the study of homopolymer blends and copolymer melts

67%

Aksimentiev A. , Hołyst R.

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tom T. 46, nr 5

307-323

EN

The Euler characteristic is applied to study the phase separation/ordering phenomena occurring in polymer mixtures. Several methods used to compute Euler characteristics are described and discussed in terms of accuracy and efficiency. A novel, robust and exact algorithm based on simplex decomposition is presented. The simulated morphology of spinodal decomposition and the phase equilibrium diagram of gradient copolymers are analyzed in terms of Euler characteristics. Again, the Euler characteristics are applied to specify the connectivity of bicontinuous patterns, to distinguish the disperse and the bicontinuous morphologies, and to detect the percolation transition. During the spinodal decomposition, the dynamic transformation between the bicontinuous and the droplet patterns is shown to involve the formation of a transient "cylindrical" morphology.

PL

Opisano metody badania kinetyki przemian fazowych za pomocą charakterystyki Eulera. Metody te zastosowano do zbadania rozpadu spinodalnego (procesu separacji faz) w dwuskładnikowej mieszaninie homopolimerów oraz do omówienia diagramu fazowego kopolimerów gradientowych. Charakterystykę Eulera wykorzystano do opisania dwuciągłej morfologii i jej przejścia w morfologię kropelkową w procesie separacji faz oraz do określenia stopnia połączenia domen powstających w tym procesie. Stwierdzono, że w procesie separacji faz struktura dwuciągła może rozpaść się na cylindryczne domeny, które w dalszej ewolucji przybierają kształt sferyczny. Omówiono także kilka metod numerycznego obliczania charakterystyki Eulera oraz przedstawiono nowy ścisły algorytm jej obliczania.